This is a great thread!
I work at an Army jet engine test facility, where we run Army T700-GE-701C's, 701D's, Navy 401C's, Army T55-L/GA-712/714's, and an Army GTCP36-155 APU out of the Apache. (I ran the -155 today, in fact.) We stock 23699 by the 55 gallon drum.
My comments!
HTS. The Army does seem to have type HTS in the system. We prefer not to use HTS and have taken a liking to Mobil Jet Oil II.
The OCI question is interesting - most of the engines we've tested burn enough oil that changing oil is sort of silly proposition. I seem to recall that a T700 will use a quart about every 20 to 25 hours and be in limits for consumption, and with a 7 or 8 quart sump (I forget), you're on fresh oil pretty quickly. We did a long test for NAVAIR on a 401C where they did ask for an oil change and analysis at some point. Not sure what they found in the analysis, we just changed the oil and pulled the sample.
Hot end seals - on the T700, and I assume the T55, most of the seals are pressurized with bleed air, so even if the seals leak, you're leaking from the high pressure side (oil sump) to the hot side. You don't get flow the other way. I've never seen oil in a turboshaft change color from contamination. This makes sense - if you keep out the contamination products from combustion, the oil will stay pretty darn clean.
There is an urban legend that notes that the T700 oil filter is so fine that the oil in the can is dirtier than whats in the engine after one pass.
thanks much,
ben